1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to providing linear position (LPOS) estimations.
2. Description of the Related Art
Data loss is a threat to companies of all sizes; however, often data loss is not the result of a big disaster, but rather is caused by human error, viruses, and disk malfunctions. A backup routine can provide protection against data loss of all kinds. In addition, tape technology remains an efficient and cost-effective means for performing system backup. Tape technology provides benefits over other types of backup in terms of cost and capacity for data storage.
Tapes drives make backup fast, easy, reliable and affordable. Speed is important because data is constantly growing while the time available for backup is shrinking. Known tape drives write between 1 MB per second and 30 MB per second. Thus, a 200 GB backup can be completed in less than two hours. Additionally, tape drives offer a range of media that allow back up of all the data on a small to medium-sized server. Tape backup also captures system setup information, as well as data, allowing an entire system to be restored in the event a disaster strikes. In addition, backups can be scheduled to occur automatically at a time determined to be most convenient.
One issue that relates to tape backup is due to a proliferation of formats and technologies relating to tapes. LTO Technology (Linear Tape-Open Technology) has been developed to combine the advantages of linear multi-channel bi-directional tape formats with enhancements in the areas of timing-based servo, hardware data compression, optimized track layouts, and high efficiency error correction code to maximize capacity and performance.
Known LTO tapes use a tape format that has longitudinally pre-written servo tracks. The servo tracks provide a timing-based track-following position error system. With the LTO tape format, longitudinal position (LPOS) information is encoded into a servo track of the tape media. On these tape formats, this information is encoded into a pair of five servo stripes, defined as the servo sub frame 1, by shifting the second and fourth stripes in these stripes. LPOS bit 1 or 0 is encoded in each servo frame. For example, FIG. 1, labeled Prior Art, shows an example of LPOS bit information.
With LPOS tape systems, the LPOS information is used for synchronization between a logical data position and a physical tape position. Additionally, the LPOS information is used for position control and velocity control within a tape transport system. Thus, a tape drive system is often required to detect LPOS information with robustness to avoid any misdetection error due to media defect, etc. Also, for data integrity, the tape drive system often can only write data if the LPOS information is correctly detected so that the data can be reliably recovered. If the LPOS information is not detectable, the tape drive system might not be able to lay data down onto the tape.